1. Field of the Invention
The present invention relates generally to orthopedic surgery, and more particularly to a system and method for performing replacement or arthroplasty of a ball and socket joint.
2. Description of the Background of the Invention
There are two major types of ball and socket joints in human anatomy, two hip joints and two shoulder joints. There are a number of surgical approaches to repair of these ball and socket joints. For the hip joint, total hip arthroplasty (THA) or replacement surgery is used to provide increased mobility to patients who have significant problems with one or both of their hip joints, including injury, arthritis, bone degeneration, cartilage damage or loss, and the like. The classic THA surgery involves the dislocation of the hip joint following an incision to access the joint. Following dislocation of the joint, the femoral head is removed from the femur by cutting the femur through the femoral neck. The hip socket or acetabulum is then reamed out using a power tool and reaming attachment to remove the cartilage remaining within the acetabulum and to prepare the acetabulum to accept the acetabular implant component or cup. Typically, the reamer attachment is sized to prepare the acetabulum to accept a particular type of implant cup or component. The implant cup is held in place by cement, special screws and or by a mesh that accepts bone growth to firmly affix the cup to the pelvis.
The femur is then prepared by reaming the femoral canal using specialized rasps or similar instruments to shape the femoral canal to accept the fermoral stem implant. The femoral stem implant is then placed in the reamed out canal and affixed in place in a manner similar to the acetabular cup. The last step in the classic procedure is to attach a metal ball to the stem to act as the hip pivot point within the cup.
For the shoulder joint, total replacement surgery is less common, and typical replacement surgery may only replace the ball of the humerus and often does not involve any cup implant. In this case, the surgery typically will replace the ball of the humerus and sometimes make various levels of modification to the surface of the glenoid socket.
Because the relative size and configuration of the implants can affect the length and offset of the leg or arm, care must be taken in the choice of the particular implants chosen. In addition, care must be taken in reaming out the socket, whether the glenoid or the acetabulum, at an appropriate position/orientation to achieve desired kinematics. Often, prior to affixing the permanent implants in place, trial implants are placed in position to assist the surgeon to gauge the impact of the replacement surgery on the patient's mobility, range of motion, and quality of life. These issues include for the hip joint, making sure the leg length closely matches the length of the non-operative leg, making sure the offset of the replacement hip joint is satisfactory so that the appearance of the leg matches the non-operative leg, and making sure the replacement joint is sufficiently stable so that normal activity by the patient will not cause the hip to dislocate or cause the leg not to be able to properly support the patient during walking and other normal routine activities. For the shoulder, the length of the arm, the offset, and range of motion of the arm and shoulder must match the non-operative arm and shoulder and the operative shoulder must not dislocate under normal activity. One concern with the use of trial implants is that these trial devices are used after all preparation of the bone has taken place. If the trial indicates that the depth of the preparation is too great the surgeon is left with using implants of a different configuration to attempt to address the situation. This requires having a greater inventory of implants on hand before the surgery begins in order to address contingencies that may occur.
In addition, the classic surgical technique presents the surgeon with a number of other challenges. The use of surgical navigation and appropriate pre-surgical planning can minimize these challenges, but even with the use of these tools, care must be taken to insure appropriate modifications to the bone are made during the surgery. For instance with hip replacement surgery, it is necessary to prepare the acetabulum to a suitable depth to accept a certain acetabular implant cup, but at the same time avoid violating or compromising the medial wall of the acetabulum. At the same time, it is necessary to make sure that the acetabulum is prepared to properly accept the implant cup. If the cup does not sit well within the prepared acetabulum, for instance, if the prepared acetabulum is deeper than the depth of the cup or the cup can not be placed sufficiently deep within the acetabulum, the cup will either become loose over time or the pelvic structure may be damaged as the cup is impacted into place. There can be similar concerns for the shoulder if the glenoid is resurfaced or modified.
In addition to concerns relating to limb length and offset mentioned above, many surgeons may rely on mechanical guides to orient implants in position relative to the patient's anatomy, which can result in imprecise and less than optimal joint function. Lastly, the surgeon must rely on experience to assess the finished range of motion and stability of the completed joint and the consequent potential for the joint to dislocate under normal everyday activities.